Process for coating paper



Jan. '15, 1952 w. H. BARRETT ET AL PROCESS FOR COATING PAPER Original Filed May 24, 1945 5 Sheets-Sheet l s .L had nrs nB IH .m m w u. 5 WEB Attorney.

Jan. 15, 1952 w. H. BARRETT ET AL PROCESS FOR COATING PAPER 5 Sheets-Sheet 2 w m w m w A. n m m w m I m m m 0.5 A w as y llllllllll /H/ I |||||Ill\\\ l I I I l|4|"||l\ Original Filed May 24, 1945 W. H. BARRETT ET AL PROCESS FOR COATING PAPER I 5 Sheets-Sheet 4 F1374 InvenboES: William. H.Bar-r-e'bt A'b'tor-ney.

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Patented Jan. 15, 1952 UNITED PATENT OFFICE 1'946-,userial No; 6735144 cit-ins; (o1. nt 1 11 1. This invention relates to' new and useful inrprovements in coating and particularly seekst0 provide a novel method and apparatus for-apply ing a smooth and uniform coating toa continuously moving web of: paper orthe like.

The present invention is particularlyconcerned with a paper coatin apparatus and process to produce coating superior in respect to smooth ness, freedom from imperfectionsetca The base stock in web form may'be of any suitable kind and the ingredients contained in the coating applied thereto may be chosenfrom a number of different materials. The c0atingmixture may include clay, calcium carbonatasatin white, etc, and an adhesive or binder such as starch, glue, casein or other suitable material all contained in an active dispersion.-

It is an object of the invention to apply a eoat ing upon a fast traveling web of paper, and the term paper" as used herein is intended to include any and all materials in web iormwhereon a coating may be applied and treated in accordance with the present invention, and no'distinction is intended by the various classes of paper such as, for example, printing, photographyyor other papers.

One procedure which-may be and has; beerremployedin coating 2. web of paper is broadly to apply coating composition to the Web in greater quantity than is required to-produce the desired weight of coating, and then to remove the excess part by the use of wipingor smoothi-ng; device such as blades or doctor rolls- Heretofore in followin the normal procedure in'applying coating to a moving web of paper considerable diiiiculty has been encountered as a result of a formation or niultiplicity of imperfections in the applied coating. tions are generally caused as aresult of a passage of a weaving web of paper to which an excess-oi coating composition has beenappliedover some form of smoothing. or wiping device;

According to this invention a uniform film' ofcoating composition may be'applied tonne-side of the paper web while the web is' firml-ysupported on the reverse sideby a -sultable --suppert'- ing means. It will be observed that-the-apparatus in this instance comprises one or more units for treating each side of the paper. The apparatus may be employed to affect thecoating of paper from which a greater portion -of moisture has been removed and generallysuperiorre: sults are obtained where the paper beingacoated contains about 3% to about l0% ol-moisturer So far asthe coating apparatus is concerned, it may These imperfec' tied l and this abili'iitidn M81) 29;

be made to operate satisfactorily on paper having' widevariations in moisture content and may be applied to 'various' types of webs.

With-the foregoing? and other objects in view, the natureof which will become'more apparent, the inventiori will be more fully understood by reference to'the drawing; the accompanying detailed description, and the'appended claims;

In the drawing; which illustrates an embodiment of the invention:

Figure-*1 diagrammatically represents in elevatioxi'oneformof the apparatus adapted to apply two coatings of the material to opposite sides of thewebs Figure I 2 is a side View with parts broken away oi a form of' a single coating unit. I

Figure3is-a side view of a coatin unit showinglmeans for applying pressure between the various rolls and the means for separating these rolls.

Figurelisa i'ront View and elevation of the coating fountain with the rolls removed.

Figurep is a side view with parts broken away Of'a coating-fountain; and

Figure dis a view taken along line 6-5 of Figures: 7

Refrriii' to the drawing, a ape web If is wit drawn from a suitable roll I 0 'and'pa'sses over Th roll'iZis supported by arm'l3 and giwebfoi paper; The paper passes over the wirim andbetween tensionin'grolls i5 and is, andf't ewebfof pap'er'passes over rolls IT and 2! before reaching the"co'a' ting "unit;

Itfoiteii ocoursthatpaper having a moisture content ofabout3%' toa b'out'l0% is resistant to tneabsorptione: moisture and-thus the coating material doesnot uniformlywet the paper. This results in a nonuniform-- coating being applied te -the web? This mneuity'may b'e overcome by lightly brushing the surface of the paper just pi "r t'o *the appl'icatlon oi the coatin i material. N-s'uitable way-'of-"aceomplishing the foregoing is to softlybrush the paper surface by rotating These-brushes preierably should rotate pbsite di rection to the travel of the web, andwhile'th'e' web is: under tension. If the web is nbt'=-uncle'r sufficient tension when it passes betweenthebr-ushes i3, additional tension may be applied. y relli9 which is supported by armsiil.

Th'epaperweb is supported by rotatable rolls 22 when theccating isapplied by applicator roll 23:-=- The' coatinglmaterial is supplied to thecontamer-18 from' a suitable sourceo'f supply (not shown. The coatingmaterial is withdrawn from the-coatin gacontainer-through pipe 29* by: means n'ge'd that tensionfis maintained upon the of pump 30 and then forced through pipe 3| in the fountain 21 by pump 30 and the material being forced into the fountain and maintained in the fountain under superatmospheric pressure. A head of the coating material is maintained above the lower nip formed by the metering roll 26 and the applicator roll 23 so that a surplus of coating material is supplied under pressure at the nip of the said rolls. This may be accomplished by connecting member 32 in the supply pipe 3|. The coating material is fed to the fountain 21 which has the open top closed by applicator roll 23 and metering roll 26. Positioned above the applicator roll 23 is smoothing roll 24 and there may be positioned above the smoothing roll a roll 25. One of the purposes of the roll 25 is to aid in cleaning the surface of the smoothing roll. It is essential that the smoothing roll surface be clean at the time it is carrying out its function of smoothing the coating upon the applicator roll.

The paper after receiving the coating, passes over suitable drier or driers such as 33, 34, and 35, and then over roll 43. It has been discovered that a smoother and more uniform coating is obtained when the coating on one side is made by two or more applications and at least partially dried between each application.

The four coating units shown in Figure 1 are similar in construction and are indicated generally at 36, 31, 38 and 39. The paper after leaving the driers 4|, 42 and 43 passes over roll 46 and then the opposite side receives the coating material either in two or more applications. After receiving the first and second application of coating on the second side, the paper passes over driers :15, 45, and 41 and after the last application of coating material, over driers 49, 50 and The paper after leaving the last drier passes over roll 52 and is wound into suitable roll 53.

In Figure 2 is shown a single coating unit in which the roll 22, 23, and 26 are of about the same diameter. For the most satisfactory results there should be a differential hardness between rolls 22 and 23, between rolls 23 and '26 and between rolls 23 and 65. The coating material is supplied to container 28, which container has an agitator or screw conveyor which keeps the material in motion, thus preventing dead spots in the coating material. The coating material is withdrawn from the container 28 by pump 3%? through means 29 and forced into the coating fountain 21 through pipe 3!. Positioned in the pipe 3| is a suitable means 55 for removing any heavy or foreign particles that may be contained in the coating material.

It is important that the temperature of the coating material does not substantially vary. For example, a variation of temperature greater than ten degrees will cause the viscosity of the coating material to change and thus result in a variation in the coating material applied to the web of paper. To hold the temperature of the coating material constant, a temperature control means 56 such as a cooling device is so positioned that the pipe 3| passes therethrough. The temperature of the coating material should be maintained below the point where skinning starts. The skinning point varies with the different kinds of coating compositions. The coating composition after passing the temperature control means passes to a member which maintains a head above the lower nip formed by the constant motion in the fountain.

Secured to the upper wall of the fountain in sealing blade 62 carried by suitable support 6|. Also secured to the open side of the fountain is member 63 which supports sealing doctor member 64. The purpose of the doctor member 54 is to seal the fountain and at the same time clean the surface of the metering roll 26 as it leaves the position of the fountain where the coating material contacts this roll. When it is desired to change the coating color or shut down the coating apparatus, any coating material left in the fountain 21 is removed by opening suitable drain 60 positioned in the bottom of the coating fountain. The drain is normally closed by a suitable cut-off valve. The coating fountain as shown in Figure 2 has a partly rounded bottom and with the coating being forced into the fountain and following the path shown by the arrows prevents any dead spots in the coating in the fountain.

The coating material is picked up by the applicator roll 23 and the amount carried by this roll is determined by metering roll 26. The coating material then passes over the surface of the smoothing roll 65 which eliminates any blemishes which might be contained in the film of coating material on applicator roll 23. Any coating material that may be picked up by the smoothing roll 65 is removed from the surface of this roll by suitable doctor 66. The material removed by the doctor 66 is returned to the coating supply by any suitable means, for example, trough 61.

To control the pressure applied to the smoothing roll surface, suitable air diaphragm loading device 68 is provided and this is connected to the smoothing roll shaft through means 69. For separating the smoothing roll from the applicator roll there is provided lift arm 10 which may be connected to any suitable lift means such as a motor, and this arm 10 is connected to the shaft of the smoothing roll 65 at H. Any coating material that may have accumulated on the backing roll is removed by a suiable doctor blade IE9 and returned by trough H0 or other means to coating supply container.

In Figure 3 is shown a modified form of coating unit in which means of separating the metering roll from the applicator roll and the backing roll from the applicator roll and the smoothing roll from the applicator roll. This same means may be utiized for'varying and controlling the amount of pressure between these rolls. It is to be understood that the means for separating the rolls may be used .with the coating units shown in Figures 1 and 2. This is essential as it tends to control the amount of coating applied to the paper and facilitates cleaning of the coating unit after any particular run or when the coating color is to be changed.

The backing roll 22 is supported by a mem ber 82 which is hingedly mounted at 83. From member 82 extends a substantially horizontal arm 84' and to this member near its outer end is connected piston 86 which is part of pressure cylinder 85. The pressure cylinder 85 is hingedly connected at 85. This cylinder permits the control of pressure-as applied by the backing roll agusegeoa and applicator roll and provides: meansion sen arating the applicator roll and the backingroll; Should any coating: be transferred to thelsurface of the backing roll 22- the'coating: isremovedby suitable doctor l08 and the removed coating material is carried away by trough I01.

The applicator roll is supported bysuitable members 317 and thisroll 2'3has-a coveringthat has resilient properties; The coveringv may be of" rubber, synthetic or natural, in factanymateral that has resilient properties. B'yproviding the applicator roll with'a covering thathas:resil ient properties a superior coating is produced;

The metering roll 2s is' -movably' supported by members 75, which. members. are hingedlyconnected at it. To -arm 1 1, formed'as a part'of 'thesupporting member 45 is pressure cylinder 18". This pressure cylinder is hingedly' connected at B3. Thepressure cylinder 101s used for'thepurpose of controlling the pressure applied between the metering roll and the applicator roll" as well as for quicl; separation of the metering roll and the applicator roll. There is provided a" suitable adjustable means between the rolls 23 and" 26and this means is composed of" members 12 and I3 and internally threaded member T4. This'suitable means can be adjusted so as tocontrol' the space distance between themetering roll andthe applicator roll so that-the amount of coating remaining on top of" the applicator roll is controlled. Positioned above the applicator roll is smoothing roll 24 and any coating picked up by the smoothing roll is removed from the-roll surface by the doctor blade 65(a) and the removed coating material is returned to the-coatingcontainer through suitable catch pan or" trough 61.

Apressurerideroll 25 is mounted above the smoothing roll and in contact with the smoothing roll surface. The pressure and-riding roll" is adapted to rotate in the same direction to'tha-t of the smoothing roll and the riding roll speed is so controlledthat any-tendency of the smoothing roll 24 to whip or to assume a position diiferent from that selected can be controlled.

Connected to the.- smoothing rollv shaft: is arm 83 which has connected to its outer-end at 89 two pressure indicating-scales 90.. If the smoothing roll tends to move in either direction from its normal position this movement is indicated on the'scales 90. By changing the speed of rotation of the riding roll thetendency of the smoothing roll to move from its normal position is overcome. Means are provided'for" loading pressure on the riding roll and this is accomplished by air diaphragm member 9-l which is connected through means 92 to the shaft of 'the riding roll. For separating the smoothing roll from the applicator roll andthe riding rollfrom thesmooth ing roll there is providedmotorrod 94 which is connected at 95 to the shaft of the riding: roll, andat 96 to arm 80. g

A fountain 27 is preferablv-supported by members ii? in proper relationship to the applicator iii roli 23 and roll 26.. The open-top of. theiountain operatively connected: to the dike supports: Secured to the outer endof thedikeadjus tingscrewis handle wheel Hi5 for adjusting the position of the dike. Mounted' on theinner side-of'the-dike are members Hi'a which cooperate with the seal ing blade 52 and seal in'the fountain in any as justed position of the dike.

To permit adjustment of? and positive contact between seal member Stand the surface of the metering roll 25. there is provided. adjustable doctor" pull rod 9.0v having: handle wheel 99 mounted near. the. outer" end thereof. Spring. I00

is mounted onathe-pull rod 98 f0.r:maintaining; the

member 69in positive contact with thesuriaceoithe; metering, roll. The, pull rods are connected to seal. member. 64 at.l0l.

The apparatus may beused with coating composition having a solidcontents varying over con siderable range. but applicants process requires that the coating compositionhave a solid contents in excess of. about 60% to. about Applicants. co -pendin:= application, Serial. No. 511,754, filed November 24, 1943, now U. S. Patent No. 2,532,141 for Process of Coating Paper, points out that mineral'" adhesive coating composition having a solid contents in excess of'60% has thixotropic charactcristics.

way of example the process may be carried out:

The surface of the movingweb" to be coated-is brushed while the paper is under tension and-the paper then passes between the applicator roll 23 and'the backing roll 22. A coating material is pickedup by the applicatorroll surface-from the fountain 2-1 and the metering roll controls the amount of coating'material that the applicator roll will carry oif to the smoothing roll. The smoothing roll then removesany surface defect that may be in thezooating-film andthereafter the film is transferred to the paper while supported on the-backing roll.. The film of coating material-isthen driedand the secondapplication of coatingmaterial is applied to the same side. Thereafter in like manner the coating material isapplied to the opposite side'of the sheet.

Selected amounts of coating materialis appliedto the sheet, and this is accomplished by controlling the shearing speed between the metering roll and. the applicator roll. For ex ample, at a shearingspeedof' 1,300 feet permin ute a coating weight per ream of about nine pounds is obtained by each coating application while at a shearing speed of about 1 ,500 feet per minute about three poundsofcoating per ream is-obtained by each-coatingapplication. It has been discovered that thecoating weight can be more sharply controlled if the shearing speed between: tlie meteringroll and the applicator roll and between the-smoothing roll and the applicatorroll is controlled. Asthe-shear-ing-= speed is increased the coating-weightperream of paper is decreased. The shearingspeed isthe sumof the speed of the applicatorroll' and'the metering rolllandlikewisethe sumof the speed ofthe applicator roll and the smoothing roll.

Tothose skilled in'the art manymodifications and widely different" embodiments and applica tions of the invention in the generalfield' of coatingwill be readily apparent. It should'be under stood that the details of our preferred process as described may be subject to some change without departing from either the spirit or scope of the invention. It is intended that the invention is not to be restricted to specific preferred embodiments, minor details, or specific modes of operation, other than is necessitated by the prior art and the appended claims. This is a division of application, Serial No. 595,618, filed May 24, 1945, now U. S. Patent No. 2,513,394.

What we claim:

1. The process of coating paper which comprises continuously flowing coating of high solid contents to a body of coating material, maintaining the temperature in the flowing coating composition substantially constant, maintaining a body of coating composition under pressure greater than atmospheric pressure in the area formed by a first and a second rotatable surface, said coating composition comprising mineral pigment and an adhesive having a solid content in excess of 60% and being of a thixotropic nature, the first rotatable surface moving in a direction opposed to the second rotatable surface and the first rotatable surface moving at a speed below that of the second rotatable surface, whereby a controlled amount of coating material is spread on and carried by the second rotatable surface, smoothing the coating material carried by the second rotatable surface by a third rotatable surface moving in the opposed direction to the surface of the second rotatable surface, and then transferring the smooth film of coating material to a moving web of paper moving in the same direction as the direction of the second rotatable surface under rolling pressure.

2. A process of coating a traveling web of paper with about three pounds and upwards per ream with a smooth film of mineral pigment and adhesive coating composition having a solid content in excess of 60% and being of a thixotropic nature, comprising the steps of maintaining a body of the coating composition under pressure and agairmt a rotatable applying surface, flowing coating composition to the body of coating composition, maintaining the temperature substantially constant in the high solids coating composition flowing to the said body of coating composition, spreading coating composition on the rotatable applying surface, applying shearing action to the coating on the applying surface, smoothing the coating on the applying surface and then bringing a moving web of paper into contact with the smooth film on the applying surface to transfer the smooth film on the paper under rolling pressure.

3. A process of coating paper containing about 3% to of moisture with an aqueous mineraladhesive coating composition having a solid content in excess of 60% and being of a thixotropic nature, which comprises lightly brushing a moving web of paper prior to the application of coating thereto, maintaining a body of said coating composition under pressure and against a rotatable surface, flowing coating composition to the body of coating composition under pressure, maintaining substantially constant temperature in the coating composition flowing to the body of coating composition, spreading and applying shearing action to coating composition on the rotatable surface by a rotatable doctor surface moving in the opposite direction and at a lesser speed than the rotatable surface, smoothing the coating on the rotatable surface and then transferring the smooth film to a moving web of paper under rolling pressure. I 4. A process of applying a smooth film of mineral pigment and adhesive coating composition to a moving web of paper comprising substantially constant flowing coating composition having a high solid content in excess of 60% and having a thixotropic nature to a body of coating composition, maintaining substantially constant temperature in the flowing coating composition whereby the temperature of the high solids coating composition varies less than about 10 F., maintaining a body of coating composition against a rotatable surface and under pressure greater than atmospheric pressure, spreading coating on the rotatable surface, applying shearing action to the coating on the rotatable surface, smoothing the coating on the rotatable surface and then transferring the smooth film of coating to a moving web of paper under rolling pressure.

5. The process of coating paper which comprises maintaining an aqueous mineral and starch adhesive coating composition under pressure greater than atmospheric pressure and against a rotatable applying surface and a rotatable doctor surface, said coating composition having a solid content in excess of 60% and being of a thixotropic nature, flowing coating composition to said body of coating composition, maintaining substantially constant temperature in the said flowing coating composition, spreading coating composition on the applying surface by said rotatable doctor surface moving in a direction opposed to and at a lesser speed than the applying surface whereby shearing action is applied to the coating composition on the applying surface, smoothing the coating composition to a smooth film on the applying surface and then transferring the smooth uniform film to a moving web of paper.

WILLIAM H. BARRETT. BERNARD K. ASDELL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,310,818 Wood July 22, 1919 1,472,230 Plum Oct. 30, 1923 1,644,451 Smith Oct. 4, 1927 1,921,368 Massey Aug. 8, 1933 1,933,963 Bradner Nov. '7, 1933 2,118,152 Bryce May 24, 1938 2,256,853 Schwartz Sept. 23, 1941 2,293,125 Fanselow Aug. 18, 1942 2,293,690 Harrigan Aug. 18, 1942 2,321,939 Quinn June 15, 1943 2,405,056 Barrett Aug. 20, 1946 2,406,057 Barrett Aug. 20, 1946 2,425,231 Dickerman et al. Aug. 5, 1947 OTHER REFERENCES Manufacture of Pulp and Paper, 3rd ed., published by McGraw-Hill, 1938, vol. 4, section 5, pp. 43 and 45.

The Manufacture of Pulp and Paper, 3rd ed, 1939, volume 5, part 4, pp. 9 and 10. 

